@article {1567,
	title = {Diversity in the weapons of sexual selection: horn evolution in the beetle genus Onthophagus (Coleoptera: Scarabaeidae)},
	journal = {Evolution},
	volume = {59},
	number = {5},
	year = {2005},
	month = {Jan},
	pages = {1060-1084},
	abstract = {Both ornaments and weapons of sexual selection frequently exhibit prolific interspecific diversity of form. Yet, most studies of this diversity have focused on ornaments involved with female mate choice, rather than on the weapons of male competition. With few exceptions, the mechanisms of divergence in weapon morphology remain largely unexplored. Here, we characterize the evolutionary radiation of one type of weapon: beetle horns. We use partial sequences from four nuclear and three mitochondrial genes to develop a phylogenetic hypothesis for a worldwide sample of 48 species from the dung beetle genus Onthophagus (Coleoptera: Scarabaeidae). We then use these data to test for multiple evolutionary origins of horns and to characterize the evolutionary radiation of horns. Although our limited sampling of one of the world{\textquoteright}s most species-rich genera almost certainly underestimates the number of evolutionary events, our phylogeny reveals prolific evolutionary lability of these exaggerated sexually selected weapons (more than 25 separate gains and losses of five different horn types). We discuss these results in the context of the natural history of these beetles and explore ways that sexual selection and ecology may have interacted to generate this extraordinary diversity of weapon morphology. },
	keywords = {Adaptive radiation, beetle horns, character divergence, male competition, Onthophagus, phylogeny, sexual selection, weapons.},
	author = {Emlen, Douglas J. and Marangelo, Jennifer and Ball, Bernard and Cunningham, Clifford}
}
@article {2037,
	title = {Trade-offs during the development of primary and secondary sexual traits in a horned beetle},
	journal = {The American Naturalist},
	volume = {163},
	number = {2},
	year = {2004},
	pages = {184-191},
	abstract = { Resource allocation trade-offs during development affect the final sizes of adult structures and have the potential to constrain the types and magnitude of evolutionary change that developmental processes can accommodate. Such trade-offs can arise when two or more body parts compete for a limited pool of resources to sustain their growth and differentiation. Recent studies on several holo- metabolous insects suggest that resource allocation trade-offs may be most pronounced in tissues that grow physically close to each other. Here we examine the nature and magnitude of developmental trade-offs between two very distant body parts: head horns and geni- talia of males of the horned scarab beetle Onthophagus taurus. Both structures develop from imaginal disklike tissues that undergo ex- plosive growth during late larval development but differ in exactly when they initiate their growth. We experimentally ablated the pre- cursor cells that normally give rise to male genitalia at several time points during late larval development and examined the degree of horn development in these males compared to that of untreated and sham-operated control males. We found that experimental males developed disproportionately larger horns. Horn overexpression was weakest in response to early ablation and most pronounced in males whose genital disks were ablated just before larvae entered the pre- pupal stage. Our results suggest that even distant body parts may rely on a common resource pool to sustain their growth and that the relative timing of growth may play an important role in deter- mining whether, and how severely, growing organs will affect each other during development. We use our findings to discuss the phys- iological causes and evolutionary consequences of resource allocation trade-offs. },
	keywords = {beetle horns, developmental timing, genitalia, imaginal disk, Juvenile hormone, Onthophagus, resource allocation trade-off},
	author = {Moczek, Armin P. and Nijhout, H. Frederik}
}
